Railway Sleeprs

Morning all

I'm building a part raised pond - 9' x 6' - hole is dug to 4' & I'm planning
on raising the dges by another 20" or so using railway sleepers. I think new
ones will be better, cleaner & easier to use, but does anyone have any
thoughts on securing them to the ground.

Will a frame of sleepers secured with heavy duty brackets be strong enough
to hold the additional 20" of water?

Cheers